Many toxic parents compare one sibling unfavorably with another to make the target child feel that he's not doing enough to gain parental affection. This motivates the child to do whatever the parents want in order to regain their favor. This divide-and-conquer technique is often unleashed against children who become a little too independent, threatening the balance of the family system.
Toxic Parents: Overcoming Their Hurtful Legacy and Reclaiming Your Life (ed. Bantam, 2009) - ISBN: 9780307575326